Condensed Consolidated Statements of Changes in Equity - USD ($) $ in Thousands	Total	Common Stock	Preferred Stock Series D convertible preferred stock	Additional Paid-in Capital	Retained Earnings (Accumulated Deficit)	Accumulated Other Comprehensive Income (Loss)	Treasury Stock	Total Attributed To Stockholders	Non- controlling Interests
Beginning Balance (in shares) at Dec. 31, 2018		6,997,382	1,150,000				3,555,242
Beginning Balance at Dec. 31, 2018	$ 643,867	$ 106	$ 110,843	$ 1,209,805	$ (310,865)	$ (731)	$ (379,249)	$ 629,909	$ 13,958
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	72,460				72,757			72,757	(297)
Foreign currency translation adjustments	(14)					(14)		(14)
Net subscriptions (redemptions) and other	(911)			838				838	(1,749)
Reclassification from other comprehensive (income) loss	726					726		726
Cash dividends declared, preferred	(6,253)			(6,253)				(6,253)
Cash dividends declared, common	(13,228)			(13,228)				(13,228)
Repurchases of common shares (in shares)		(286,620)					(286,620)
Repurchases of common shares	(30,000)						$ (30,000)	(30,000)
Issuance of common shares related to employee stock transactions (in shares)		166,834
Issuance of common shares related to employee stock transactions	1,430	$ 1		1,429				1,430
Taxes paid on stock-based compensation	(6,601)			(6,601)				(6,601)
Stock-based compensation	16,140			16,140				16,140
Ending Balance (in shares) at Sep. 30, 2019		6,877,596	1,150,000				3,841,862
Ending Balance at Sep. 30, 2019	677,616	$ 107	$ 110,843	1,202,130	(238,108)	(19)	$ (409,249)	665,704	11,912
Beginning Balance at Dec. 31, 2018	57,481
Increase (Decrease) in Redeemable Non-controlling Interests [Roll Forward]
Total net income (loss) attributable to noncontrolling interests	3,266
Net subscriptions (redemptions) and other	30,863
Ending Balance at Sep. 30, 2019	91,610
Beginning Balance (in shares) at Jun. 30, 2019		6,944,892	1,150,000				3,770,913
Beginning Balance at Jun. 30, 2019	663,672	$ 107	$ 110,843	1,204,033	(262,193)	(7)	$ (401,748)	651,035	12,637
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	24,017				24,085			24,085	(68)
Foreign currency translation adjustments	(12)					(12)		(12)
Net subscriptions (redemptions) and other	(109)			548				548	(657)
Cash dividends declared, preferred	(2,085)			(2,085)				(2,085)
Cash dividends declared, common	(4,972)			(4,972)				(4,972)
Repurchases of common shares (in shares)		(70,949)					(70,949)
Repurchases of common shares	(7,501)						$ (7,501)	(7,501)
Issuance of common shares related to employee stock transactions (in shares)		3,653
Issuance of common shares related to employee stock transactions	5	$ 0		5				5
Taxes paid on stock-based compensation	(93)			(93)				(93)
Stock-based compensation	4,694			4,694				4,694
Ending Balance (in shares) at Sep. 30, 2019		6,877,596	1,150,000				3,841,862
Ending Balance at Sep. 30, 2019	677,616	$ 107	$ 110,843	1,202,130	(238,108)	(19)	$ (409,249)	665,704	11,912
Beginning Balance at Jun. 30, 2019	60,502
Increase (Decrease) in Redeemable Non-controlling Interests [Roll Forward]
Total net income (loss) attributable to noncontrolling interests	1,342
Net subscriptions (redemptions) and other	29,766
Ending Balance at Sep. 30, 2019	91,610
Beginning Balance (in shares) at Dec. 31, 2019		6,809,280	1,150,000				3,927,607
Beginning Balance at Dec. 31, 2019	686,257	$ 107	$ 110,843	1,199,205	(215,216)	9	$ (419,249)	675,699	10,558
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	36,496				36,642			36,642	(146)
Foreign currency translation adjustments	(9)					(9)		(9)
Net subscriptions (redemptions) and other	(1,597)			(167)				(167)	(1,430)
Conversion of preferred stock (in shares)		912,806	(1,150,000)
Conversion of preferred stock	0	$ 9	$ (110,843)	110,834				0
Cash dividends declared, preferred	$ (18,371)			(18,371)				(18,371)
Repurchases of common shares (in shares)	(239,720)	(239,720)					(239,720)
Repurchases of common shares	$ (25,000)						$ (25,000)	(25,000)
Issuance of common shares related to employee stock transactions (in shares)		130,788
Issuance of common shares related to employee stock transactions	163	$ 2		161				163
Taxes paid on stock-based compensation	(5,693)			(5,693)				(5,693)
Stock-based compensation	15,766			15,766				15,766
Ending Balance (in shares) at Sep. 30, 2020		7,613,154	0				4,167,327
Ending Balance at Sep. 30, 2020	688,012	$ 118	$ 0	1,301,735	(178,574)	0	$ (444,249)	679,030	8,982
Beginning Balance at Dec. 31, 2019	63,845
Increase (Decrease) in Redeemable Non-controlling Interests [Roll Forward]
Total net income (loss) attributable to noncontrolling interests	21,653
Net subscriptions (redemptions) and other	13,779
Ending Balance at Sep. 30, 2020	99,277
Beginning Balance (in shares) at Jun. 30, 2020		7,664,272	0				4,113,460
Beginning Balance at Jun. 30, 2020	666,511	$ 118	$ 0	1,303,036	(208,222)	(17)	$ (436,749)	658,166	8,345
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	30,625				29,648			29,648	977
Foreign currency translation adjustments	17					17		17
Net subscriptions (redemptions) and other	(340)			0				0	(340)
Cash dividends declared, common	$ (6,695)			(6,695)				(6,695)
Repurchases of common shares (in shares)	(53,867)	(53,867)					(53,867)
Repurchases of common shares	$ (7,500)						$ (7,500)	(7,500)
Issuance of common shares related to employee stock transactions (in shares)		2,749
Issuance of common shares related to employee stock transactions	49	$ 0		49				49
Taxes paid on stock-based compensation	(124)			(124)				(124)
Stock-based compensation	5,469			5,469				5,469
Ending Balance (in shares) at Sep. 30, 2020		7,613,154	0				4,167,327
Ending Balance at Sep. 30, 2020	688,012	$ 118	$ 0	$ 1,301,735	$ (178,574)	$ 0	$ (444,249)	$ 679,030	$ 8,982
Beginning Balance at Jun. 30, 2020	90,687
Increase (Decrease) in Redeemable Non-controlling Interests [Roll Forward]
Total net income (loss) attributable to noncontrolling interests	10,309
Net subscriptions (redemptions) and other	(1,719)
Ending Balance at Sep. 30, 2020	$ 99,277